House Democrats pushed forward Wednesday with an effort to delete the word “navigable” from the Clean Water Act - a change that would give the government greater ability to enforce clean-water rules but that opponents said amounts to a federal power grab.

Rep. James L. Oberstar, chairman of the Transportation and Infrastructure Committee, said he’s trying to return the law to where it was before 2001, when the Supreme Court issued the first of two rulings that said the Clean Water Act’s use of “navigable” limits the government’s oversight to major rivers, lakes and similar waterways.

Environmentalists say those rulings and subsequent George W. Bush administration regulations have been exploited by polluters.

“Clean, safe water is a right for all Americans,” said Mr. Oberstar, Minnesota Democrat. “Unless we act, the law can’t ensure that right. Because of the Supreme Court decisions, companies have spilled oil, carcinogens and bacteria into the lakes, rivers and other waters without being fined or prosecuted.”

He said his intention was to return the law to its status in 2001, which he said had the agreement of both Democratic and Republican administrations.

Both sides were still poring over the ins and outs of the legislation, but opponents said they fear the bill goes further than Mr. Oberstar is letting on.

“If this bill were to become law, there’d be no body of water in America that wouldn’t be at risk of job-killing federal regulation - from farmers’ irrigation canals to backyard ponds and streams to mud puddles left by rainstorms,” said Rep. Doc Hastings of Washington, the ranking Republican on the House Natural Resources Committee.

The Waters Advocacy Coalition, made up of farm, manufacturing and housing advocacy groups, said the bill would upset the federal-state balance that has developed on water protection.

At its core, the fight is over how broadly Congress wanted the 1972 Clean Water Act to be applied.

The law in one place says the act was to protect the nation’s waters, but in other places, it says it’s meant to govern “navigable” waters. The Supreme Court ruled that constrained the Environmental Protection Agency to regulating waterways big enough for ship traffic.

Paul Schwartz, national policy coordinator for Clean Water Action, a lobby group, said that has meant polluters just have to go upstream until they find a waterway no longer covered under the law, and they can pollute.

Mr. Oberstar has introduced similar legislation before but said he has tried in this version to meet the concerns of previous opponents. He said he specifically has exempted groundwater and wastewater and has lifted key language about the definition of water from farm regulations on which all sides already agree.

Mr. Schwartz said folks on his side weren’t thrilled with some of the exemptions but said it shows Mr. Oberstar is making a good effort, and he said he doesn’t understand those who remain opposed.

“I think our opponents are just in some weird place where they’re frantically trying to fix the facts to the conclusion they’re trying to drive,” he said. “What is it that they think they’re going to gain politically and otherwise by being against motherhood and apple pie?”

The chances for the bill are uncertain.

A Senate committee already has passed a similar bill, but it has not received a full Senate vote. Mr. Oberstar said he wants to have the measure on the House floor in September and said the chamber’s leaders have promised to carve out debate time.

Mr. Oberstar said he doesn’t know how much more water would fall under the federal government’s scope under his bill.

The measure is being co-sponsored by two congressman from Michigan, a Democrat and a Republican, who said they are particularly interested in trying to protect waters that feed the Great Lakes.